In centrally controlled telecommunication switching systems, more particularly telephone switching systems, subscriber lines and/or interexchange trunks from or to switching centers are interconnected by switching elements (crosspoints) forming in their entirety a switching network in accordance with the connections needed tor each a given destination. This arrangement of the switching elements within the switching network is likewise referred to as the trunking scheme of the latter. Among the possible trunking schemes of telecommunication switching systems one can distinguish various types. One such type includes switching networks with stage-by-stage call buildup, which are divided into several ranks of selectors and in which during (stage-by-stage) call buildup only the possible paths within the rank of selectors currently being reached are taken into account. Another type includes switching networks with conjugate selection in which for a call buildup the busy/idle status of the entire switching network is taken into account.
In the case of switching networks with conjugate selection a distinction can be made between switching networks having an elongated trunking scheme, in which on two sides of the switching network there are disposed two groups of terminals and connections can be established only between one terminal of one side and one terminal of the other side, and switching networks with reversed trunking scheme, in which all terminals are located on the same side of the switching network. Switching networks using the reversed trunking scheme are disclosed, for example, in Reports on Telephone Engineering VI (1970) 1/2, published by Siemens A.G., Berlin and Munich, West Germany, pp. 28-33 and 65-73. (cf. British Pat. No. 1,058,893) have the advantage of practically full availability to the outgoing lines, a high flexibility with respect to different conditions of compatibility and a far-reaching modular structure. However, the individual components of prior art space-division switching networks with the reversed trunking scheme and crosspoints formed by dry reed contacts in metal enclosures cannot be made by the increasingly popular large scale integration techniques. Difficulties are encountered, such as the so-called pin limitation, excessive heating, and technological limits which possibly allow one to place, e.g., a matrix with 4 . . . 16 crosspoints on a single component in medium scale integration.
An object of the invention is to provide a switching network having reversed trunking which can be constructed using large scale integration techniques, whereby several hundred switches can easily be placed on a single component.